Dielectric barrier discharge lamp configured as a double tube

ABSTRACT

The invention relates to a dielectric barrier discharge lamp in a coaxial double-tube arrangement, comprising an exterior electrode ( 6 ), and interior electrode ( 7 ), and an auxiliary electrode ( 8 ). The interior electrode ( 7 ) is designed as an electrically conductive layer placed inside the interior tube ( 3 ) of the double-tube arrangement. The auxiliary electrode ( 8 ) is designed, for example, as a metal tube or pipe and is also disposed inside the interior tube ( 3 ), specifically in direct contact with the layer. In this manner, the conductivity of the interior electrode (S) is improved.

TECHNICAL FIELD

The invention is based on a dielectric barrier discharge lamp with adischarge vessel with a coaxial double-tube arrangement, i.e. an innertube is arranged coaxially within an outer tube. In this case, the innertube and the outer tube are connected to one another at both of theirend sides and thus form the gas-tight discharge vessel. The dischargespace surrounded by the discharge vessel therefore extends between theinner tube and the outer tube.

This type of discharge lamp typically has a first electrode, which isarranged within the inner tube, and a second electrode, which isarranged on the outer side of the outer tube. Both electrodes aretherefore located outside the discharge vessel or the discharge space.In this case the discharge is therefore impeded by a dielectric barrieron two sides. When mention is occasionally made below of the internalelectrode or inner electrode and the external electrode or outerelectrode for reasons of simplicity, this designation consequently onlyrefers to the physical arrangement of the electrode in question withrespect to the coaxial double-tube arrangement, i.e. within the innertube or on the outer side of the outer tube. In this case, the twoelectrodes should bear as tightly as possible against the wall of thedischarge vessel in order for the dielectrically impeded discharge to beas uniform as possible in the discharge space.

This type of lamp is used in particular for UV irradiation in processingtechnology, for example for surface cleaning and activation,photolytics, ozone generation, drinking water purification,metal-plating, and UV-curing. In, this context, the designation emitteror UV emitter is also conventional.

PRIOR ART

The document U.S. Pat. No. 4,945,290 has disclosed a coaxial double-tubeemitter. The inner electrode is in this case in the form of a metalliclayer.

The document EP 0 703 603 A1 has likewise disclosed a coaxialdouble-tube emitter. In said document, reference is made to thedisadvantages both in terms of the vapor deposition of a metallic layerand as regards the life. It is therefore obviously not possible for alayer of uniform thickness to be vapor-deposited within the constrictedinner tube of the double-tube emitter. In addition, the layer can becomedetached easily with a thickness of greater than approximately 0.01 mm.Furthermore, the layer is corroded in particular at thin points duringoperation and thus shortens the usable life of the emitter. EP 0 703 603A1 therefore proposes a metal tube as the inner electrode instead of ametallic layer, said metal tube having a straight, continuous slot inthe direction of the longitudinal axis. As an alternative, a tubularinner electrode comprising two half-shells which are spaced apart fromone another is disclosed. One disadvantage is in any case the fact thatneither fluctuations in the diameter along the inner tube norundulations and other uneven sections in the circumferential directioncan be compensated for.

DESCRIPTION OF THE INVENTION

The object of the present invention is to specify a dielectric barrierdischarge lamp with a coaxial double-tube arrangement with an improvedinternal electrode.

This object is achieved by a dielectric barrier discharge lamp with adischarge vessel, which comprises an outer tube and an inner tube, theinner tube being arranged coaxially within the outer tube, the innertube and the outer tube being connected to one another in a gas-tightmanner, as a result of which a discharge space filled with a dischargemedium is formed between the inner tube and the outer tube, a firstelectrode and at least one further electrode, the first electrode beingin the form of an electrically conductive layer applied to the innerside of the inner tube, characterized by the fact that an additionalelectrode, which is capable of carrying current and is in electricallyconductive contact with the first electrode, is arranged within theinner tube.

Particularly advantageous configurations are given in the dependentclaims.

In addition, protection is claimed for an electrical emitter system witha dielectric barrier discharge lamp according to the invention and anelectrical supply device which is connected thereto.

The basic concept of the invention consists in arranging an additionalelectrode in the inner tube of a double-tube emitter and bringing saidadditional electrode into electrically conductive contact with theelectrically conductive layer. It has been shown that the electricallyconductive layer cannot carry the current to a sufficient extent andmelts through partially in the event of very high electrical powers. Theadditional electrode is therefore designed in such a way that it cancarry some of the current during operation.

The electrical contact is preferably made by the additional electrodetouching the layer as uniformly as possible. In addition, it may also beadvantageous to provide a suitable connection medium, for example anelectrically conductive paste, an adhesive or the like, between thelayer and the additional electrode in order to further improve theelectrical contact and to maintain the electrical contact for as long aspossible.

In order that the current-carrying capacity of the additional electrodeis at its optimum, the additional electrode preferably extendssubstantially over the entire axial and/or azimuthal extent of theelectrically conductive layer, i.e. the entire outer surface thereof. Inaddition, the dimensions and shape of the additional electrode arepreferably selected in such a way that electrical contact which is aseffective as possible and covers as large an area as possible is madewith the electrically conductive layer. Otherwise, there is the risk ofincreased local current densities and therefore melting-through of thelayer, in particular at very high powers. However, the additionalelectrode does not necessarily need to cover the metallic layer of theinner tube over the entire outer surface. Instead, it may in certaincircumstances also be sufficient if the additional electrode only coverspart of the outer surface of the metallic layer, for example by ametallic strip of sufficient thickness being adhesively bonded,preferably axially parallel.

The additional electrode is preferably in the form of an electricallyconductive, substantially circular-cylindrical structure, for example inthe form of a metal tube or flexible metal tube with suitabledimensions, preferably made from a woven metallic fabric, knittedmetallic fabric or the like. This ensures that the additional electrodecan be introduced easily into the inner tube without the electricallyconductive layer being destroyed in the process. A further aspect isthat the additional electrode bears against the electrically conductivelayer as well and as uniformly as possible, preferably over the entireextent of the layer. For this purpose, it is advantageous when using ametal tube to provide said metal tube with one or more slots. It canthus adapt better to the surface of the electrically conductive layer,in a similar way to a woven metallic fabric.

The electrically conductive, for example metallic layer of the innertube consists of, for example, aluminum or a noble metal, preferablyplatinum, palladium or gold. It is applied by physical processes such assputtering, vacuum vapor deposition, electroplating or chemical coating,such as baking varnishes, chemical precipitation or electroless plating.

In order to avoid scratching the thin metallic layer of the inner tubewhen installing the additional electrode, it may be advantageous to coatthis layer in advance with a scratch-resistant protective layer, forexample consisting of nickel.

With the aid of the additional electrode which is capable of carryingcurrent, the invention makes it possible to use a metallic layer, withthe associated advantage of optimum bearing contact against the innertube, as the primary inner electrode even during permanent operation andat high electrical powers. Finally, the invention therefore proposes atwo-component solution. The first component is a thin layer and isoptimal for the bearing contact against the inner tube. The secondcomponent is an additional electrode which is capable of carryingcurrent and is primarily used for the transfer of current.

An electrical emitter system according to the invention also has anelectrical supply device in addition to the dielectric barrier dischargelamp according to the invention. The first terminal of the supply deviceis connected to the outer electrode. The second terminal of the supplydevice is connected to the additional electrode.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be explained in more detail below with reference toexemplary embodiments. In the drawings:

FIG. 1 a shows an illustration of a longitudinal section through adielectric barrier discharge lamp according to the invention,

FIG. 1 b shows an enlarged detail of the lamp shown in FIG. 1 a,

FIG. 1 c shows a cross-sectional illustration of the lamp shown in FIG.1 a,

FIG. 2 shows an additional electrode in a side view,

FIG. 3 shows a variant of an additional electrode with a longitudinalslot in a side view,

FIG. 4 shows a variant of an additional electrode with a plurality oflongitudinal slots in a side view.

FIG. 5 shows a variant of an additional electrode with a rectangularslot which is continuous in the longitudinal direction.

PREFERRED EMBODIMENT OF THE INVENTION

FIGS. 1 a to 1 c show a very schematized illustration of a side view, anenlarged partial view and a cross-sectional illustration, respectively,of a first exemplary embodiment of the dielectric barrier discharge lamp1 according to the invention. The elongate discharge vessel of the lamp1 comprises an outer tube 2 and an inner tube 3 with a coaxialdouble-tube arrangement, said tubes thus defining the longitudinal axisof the discharge vessel. The typical length of the tubes is betweenapproximately 10 and 250 cm, depending on the application. The outertube 2 has a diameter of 44 mm and a wall thickness of 2 mm. The innertube 3 has a diameter of 20 mm and a wall thickness of 1 mm. Both tubes2, 3 are made from quartz glass which is transmissive for UV radiation.In addition, the discharge vessel is sealed at both of its end sides insuch a way that an elongate discharge space 4 in the form of an annulargap is formed. For this purpose, the discharge vessel has suitablyshaped, annular vessel sections 5 at each of its two ends. In addition,an exhaust tube (not illustrated) is attached to one of the vesselsections 5 and is used initially to evacuate the discharge space 4 andthen to fill said discharge space with 15 kPa of xenon. A wire mesh 6 ismounted on the outer side of the wall of the outer tube 2 and forms theouter electrode of the lamp 1. In the interior of the inner tube 3, i.e.likewise outside of the discharge space 4 surrounded by the dischargevessel, a gold layer 7 which is approximately 100 nm thick is appliedand acts as a tubular inner electrode. In addition, a metallic flexiblefabric tube 8 made from stainless steel is arranged within the innertube 3 and acts as additional electrode. For this purpose, the outerdiameter of the flexible fabric tube 8 is selected in such a way thatthe flexible fabric tube 8 can firstly be used readily and withoutdestroying the gold layer 7 and secondly there is good and uniformcontact between the gold layer 7 and the flexible fabric tube 8. Inorder to ensure the flexibility of the flexible fabric tube 8, the wireshave a thickness of preferably less than 0.5 mm. The gold layer 7 andthe flexible fabric tube 8 both extend virtually over the entire lengthof the inner tube 3. The wire mesh 6 (outer electrode) and the flexiblefabric tube 8 (additional electrode) are each connected directly to aterminal of an electrical ballast (EB) 9 for operation of the lamp.Owing to the electrical contact with the metallic flexible fabric tube8, the gold layer 7 is consequently also connected to the electronicballast 9 via the metallic flexible fabric tube 8, as a result of whichultimately the current-carrying effect of the flexible fabric tube 8 isproduced. The electronic ballast 9 serves the purpose of starting andmaintaining a dielectric barrier discharge within the discharge space 4during operation of the dielectric barrier discharge lamp 1.

Reference is made below to FIGS. 2 to 5, which show different variantsof the additional electrode, in each case in a schematic side view. FIG.2 shows a slightly larger illustration once again of the metallicflexible fabric tube 8 used as additional electrode in FIGS. 1 a-1 c.This has the advantage that it is relatively flexible and can thereforebe inserted particularly readily into the inner tube without damagingthe gold layer 7. In addition, the metallic flexible fabric tube 8 canconform particularly well to potential uneven portions andirregularities of the inner tube 3 or the gold layer 7 and can thereforeensure particularly effective and flat electrical contact with the goldlayer 7. FIG. 3 shows a metal tube 10, which has a longitudinal slot 11,which extends virtually over the entire length of the metal tube 10,typically over approximately 9/10 of the total length. Alternatively,the longitudinal slot can also be continuous. In any case, the metaltube 10, by virtue of the longitudinal slot 11, can adapt better to themetallic layer 7 of the inner tube than in the case without a slot.FIGS. 4 and 5 show further variants of a metal tube with slots asadditional electrode. In FIG. 4, the metal tube 10′ has a plurality ofnon-continuous slots 12, which are arranged so as to overlap one anotherwhen viewed parallel to the longitudinal axis and in the direction, ofthe longitudinal axis. In addition, the slots are preferably arranged soas to be distributed over the entire circumference of the metal tube10′. Finally, in FIG. 5, the metal tube 10″ has a rectangular slot 13which is continuous in the longitudinal direction. As a result, themetal tube 10″ can adapt even more flexibly to small uneven portions ofthe inner tube or the metallic layer applied thereto.

1. A dielectric barrier discharge lamp (1) with a discharge vessel,which comprises an outer tube (2) and an inner tube (3), the inner tube(3) being arranged coaxially within the outer tube (2), the inner tube(3) and the outer tube (2) being connected to one another in a gas-tightmanner, as a result of which a discharge space (4) filled with adischarge medium is formed between the inner tube and the outer tube, afirst electrode (7) and at least one further electrode (6), the firstelectrode (7) being in the form of an electrically conductive layerapplied to the inner side of the inner tube (3), characterized in thatan additional electrode (8), which is capable of carrying current and isin electrically conductive contact with the electrode (7), is arrangedwithin the inner tube (3).
 2. The lamp as claimed in claim 1, whereinthe additional electrode (8) which is capable of carrying current isarranged in such a way that it touches the electrically conductive layer(7).
 3. The lamp as claimed in claim 1 or 2, wherein the additionalelectrode (8) which is capable of carrying current extends substantiallyover the entire axial extent of the electrically conductive layer (7).4. The lamp as claimed in one of claims 1 to 2, wherein the additionalelectrode (8) which is capable of carrying current extends substantiallyover the entire azimuthal extent of the electrically conductive layer(7).
 5. The lamp as claimed in one of claims 1 to 2, wherein theadditional electrode is a substantially circular-cylindricalelectrically conductive structure.
 6. The lamp as claimed in one ofclaims 1 to 2, wherein the additional electrode is in the form of anelectrically conductive flexible fabric tube (8).
 7. The lamp as claimedin one of claims 1 to 2, wherein the additional electrode is in the formof an electrically conductive tube (10-10″), which has at least one slot(11-13).
 8. The lamp as claimed in one of claims 1 to 2, wherein theelectrically conductive layer (7) consists of aluminum or a noble metal,preferably platinum, palladium or gold.
 9. The lamp as claimed in one ofclaims 1 to 2, wherein the electrically conductive layer has ascratch-resistant coating.
 10. The lamp as claimed in claim 9, whereinthe scratch-resistant coating consists of nickel.
 11. The lamp asclaimed in one of claims 1 to 2, wherein a suitable connection medium,for example an electrically conductive paste or an adhesive, is providedbetween the layer and the additional electrode.
 12. An electricalemitter system with a dielectric barrier discharge lamp according to oneof claims 1 to 2 and an electrical supply device (9), whose firstterminal is connected to the outer electrode (6) and whose secondterminal is connected to the additional electrode (8).